Leptospirosis is a blood infection caused by the bacteria Leptospira^[8] that can infect humans, dogs, rodents and many other wild and domesticated animals.^[8] Signs and symptoms can range from none to mild (headaches, muscle pains, and fevers) to severe (bleeding in the lungs or meningitis).^[5] Weil’s disease (/ˈvaɪlz/ VILES),^[12] the acute, severe form of leptospirosis, causes the infected individual to become jaundiced (skin and eyes become yellow), develop kidney failure, and bleed.^[6] Bleeding from the lungs associated with leptospirosis is known as severe pulmonary haemorrhage syndrome.^[5]

More than ten genetic types of Leptospira cause disease in humans.^[13] Both wild and domestic animals can spread the disease, most commonly rodents.^[8] The bacteria are spread to humans through animal urine or feces, or water or soil contaminated with animal urine and feces, coming into contact with the eyes, mouth, nose or breaks in the skin.^[8] In developing countries, the disease occurs most commonly in pest control, farmers and low-income people who live in areas with poor sanitation.^[5]

In developed countries, it occurs during heavy downpours and is a risk to pest controllers, sewage workers^[14] and those involved in outdoor activities in warm and wet areas.^[5] Diagnosis is typically by testing for antibodies against the bacteria or finding bacterial DNA in the blood.^[5]

Efforts to prevent the disease include protective equipment to block contact when working with potentially infected animals, washing after contact, and reducing rodents in areas where people live and work.^[7] The antibiotic doxycycline is effective in preventing leptospirosis infection.^[7] Human vaccines are of limited usefulness;^[15] vaccines for other animals are more widely available.^[16] Treatment when infected is with antibiotics such as doxycycline, penicillin, or ceftriaxone.^[8] The overall risk of death is 5–10%.^[10] However, when the lungs are involved, the risk of death increases to the range of 50–70%.^[8]

It is estimated that one million severe cases of leptospirosis in humans occur every year, causing about 58,900 deaths.^[11] The disease is most common in tropical areas of the world but may occur anywhere.^[7] Outbreaks may arise after heavy rainfall.^[7] The disease was first described by physician Adolf Weil in 1886 in Germany.^[17][18] Infected animals may have no, mild or severe symptoms.^[19] These may vary by the type of animal.^[16][19] In some animals Leptospira live in the reproductive tract, leading to transmission during mating.^[16]

Signs and symptoms[edit]

The symptoms of leptospirosis usually appear one to two weeks after infection,^[7] but the incubation period can be as long as a month.^[21] The illness is biphasic in a majority of symptomatic cases. Symptoms of the first phase (acute or leptospiremic phase) last five to seven days. In the second phase (immune phase), the symptoms resolve as antibodies against the bacteria are produced.^[8] Additional symptoms develop in the second phase.^[22] The phases of illness may not be distinct, especially in patients with severe illness.^[23] 90% of those infected experience mild symptoms while 10% experience severe leptospirosis.^[24]

Leptospiral infection in humans causes a range of symptoms, though some infected persons may have none. The disease begins suddenly with fever accompanied by chills, intense headache, severe muscle aches and abdominal pain.^[5][21] A headache brought on by leptospirosis causes throbbing pain and is characteristically located at the head’s bilateral temporal or frontal regions. The person could also have pain behind the eyes and a sensitivity to light. Muscle pain usually involves the calf muscle and the lower back.

The most characteristic feature of leptospirosis is the conjunctival suffusion (conjunctivitis without exudate) which is rarely found in other febrile illnesses. Other characteristic findings on the eye include subconjunctival bleeding and jaundice. A rash is rarely found in leptospirosis. When one is found alternative diagnoses such as dengue fever and chikungunya fever should be considered. Dry cough is observed in 20–57% of people with leptospirosis. Thus, this clinical feature can mislead a doctor to diagnose the disease as a respiratory illness. Additionally, gastrointestinal symptoms such as nausea, vomiting, abdominal pain, and diarrhoea frequently occur. Vomiting and diarrhea may contribute to dehydration. The abdominal pain can be due to acalculous cholecystitis or inflammation of the pancreas.^[21] Rarely, the lymph nodes, liver, and spleen may be enlarged and palpable.^[8]

There will be a resolution of symptoms for one to three days.^[7] The immune phase starts after this and can last from four to 30 days and can be anything from brain to kidney complications.^[25] The hallmark of the second phase is inflammation of the membranes covering the brain.^[7] Signs and symptoms of meningitis include severe headache and neck stiffness.^[7] Kidney involvement is associated with reduced or absent urine output.^[7]

The classic form of severe leptospirosis, known as Weil’s disease, is characterised by liver damage (causing jaundice), kidney failure, and bleeding, which happens in 5–10% of those infected.^[7] Lung and brain damage can also occur. For those with signs of inflammation of membranes covering the brain and the brain itself, altered level of consciousness can happen.

A variety of neurological problems such as paralysis of half of the body, complete inflammation of a whole horizontal section of spinal cord, and muscle weakness due to immune damage of the nerves supplying the muscles are the complications. Signs of bleeding such as non-traumatic bruises at 1 mm (0.039 in), non-traumatic bruises more than 1 cm (0.39 in), nose bleeding, blackish stools due to bleeding in the stomach, vomiting blood and bleeding from the lungs can also be found. Prolongation of prothrombin time in coagulation testing is associated with severe bleeding manifestation. However, low platelet count is not associated with severe bleeding.^[21] Pulmonary haemorrhage is alveolar haemorrhage (bleeding into the alveoli of the lungs) leading to massive coughing up of blood, and causing acute respiratory distress syndrome, where the risk of death is more than 50%.^[21] Rarely, inflammation of the heart muscles, inflammation of membranes covering the heart, abnormalities in the heart’s natural pacemaker and abnormal heart rhythms may occur.^[8]

The bacteria can be found in ponds, rivers, puddles, sewers, agricultural fields and moist soil.^[7] Pathogenic Leptospira have been found in the form of aquatic biofilms, which may aid survival in the environment.^[29]

The number of cases of leptospirosis is directly related to the amount of rainfall, making the disease seasonal in temperate climates and year-round in tropical climates.^[7] The risk of contracting leptospirosis depends upon the risk of disease carriage in the community and the frequency of exposure.^[21] In rural areas, farming and animal husbandry are the major risk factors for contracting leptospirosis.^[5] Poor housing and inadequate sanitation also increase the risk of infection.^[21] In tropical and semi-tropical areas, the disease often becomes widespread after heavy rains or after flooding.^[7]